XML DOM Traverse Node Tree

Traversing the Node Tree

Traversing a node tree means looping through, or traveling across the node tree.

The example below loops through all child nodes of <book>, and displays their names and values:

Example explained:

1. Load the XML string into xmlDoc
2. Get the child nodes of the root element
3. Loop through each child node and output the node name and the node value of the text node

DOM - White Spaces and New Lines

XML often contains new line, or white space characters, between nodes. This is often the case when the document is edited by a simple editor like Notepad.

The following example contains CR/LF (new line) between each line and two spaces in front of each child node:

The following example will output the number of child nodes the root element (of books.xml) has. Browsers will output 9 child nodes:

PCDATA - Parsed Character Data

XML parsers normally parse all the text in an XML document.

When an XML element is parsed, the text between the XML tags is also parsed:

The parser does this because XML elements can contain other elements, as in this example, where the <name> element contains two other elements (first and last):

and the parser will break it up into sub-elements like this:

Parsed Character Data (PCDATA) is a term used about text data that will be parsed by the XML parser.

CDATA - (Unparsed) Character Data

The term CDATA is used about text data that should not be parsed by the XML parser.

Characters like "<" and "&" are illegal in XML elements.

"<" will generate an error because the parser interprets it as the start of a new element.

"&" will generate an error because the parser interprets it as the start of a character entity.

Some text, like JavaScript code, contains a lot of "<" or "&" characters. To avoid errors script code can be defined as CDATA.

Everything inside a CDATA section is ignored by the parser.

A CDATA section starts with "<![CDATA[" and ends with "]]>":

In the example above, everything inside the CDATA section is ignored by the parser.

Notes on CDATA sections:

A CDATA section cannot contain the string "]]>". Nested CDATA sections are not allowed.

The "]]>" that marks the end of the CDATA section cannot contain spaces or line breaks.